Core-Based Chemostratigraphy

of the Barnett Shale, Permian Basin, Texas

 Harry Rowe¹, Steve Ruppel², Sue Rimmer³, and Robert Loucks²

¹Earth and Environmental Sciences, University of Texas at Arlington,

Box 19049, 500 Yates St., Arlington, Texas  76019

²Bureau of Economic Geology, The University of Texas at Austin,

University Station Box X, Austin, Texas 78713-8924

 ³Department of Geology, Southern Illinois University Carbondale,

207 Parkinson Lab, Carbondale, Illinois  62901

ABSTRACT

Chemostratigraphic evidence from organic-rich mudstones of south-central North America elucidates the restricted nature and paleoceanography of a deep-water depositional environment preceding the late Paleozoic Marathon-Ouachita-Alleghenian Orogeny.  Specifically, a 177-sample geochemical dataset from the Reliance Triple Crown #1 core (Pioneer Natural Resources), Pecos County, Texas, is presented and interpreted in terms of the paleoenvironmental conditions.  Using several stratigraphic geochemical proxies (organic and inorganic carbon, sulfur, iron, phosphorus, and molybdenum) and inferences from thin sections, a general pattern of deposition is developed.  Furthermore, the deep-water residence time of the Permian Basin during Barnett deposition is assessed by comparing Barnett sample geochemistry to the sediment geochemistry of modern anoxic silled basins.  Specifically, the molybdenum–total organic carbon (Mo-TOC) relationship preserved within the Barnett Formation of the Permian Basin is compared to Mo-TOC relationships in modern anoxic silled basins, providing evidence that the Barnett was deposited under enhanced basinal restriction with a deep-water renewal time of several tens of thousands of years.  Molybdenum, a trace element that is relatively abundant in seawater, is used for this comparison because it is documented to undergo enrichment in marine sediments under anoxic and euxinic (free H₂S) conditions.  The general lack of biological activity and the overall abundance of organic carbon in the Barnett Formation strongly suggest that conditions were anoxic.  The enhanced TOC, coupled with low Mo concentrations, therefore suggests that anoxia prevailed, but under much more restrictive conditions than what is currently observed in modern anoxic environments.

Rowe, H., S. Ruppel, S. Rimmer, and R. Loucks, 2009, Core-based chemostratigraphy of the Barnett Shale, Permian Basin, Texas:  Gulf Coast Association of Geological Societies Transactions, v. 59, p. 675-686.

AAPG Search and Discover Article #90093 © 2009 GCAGS 59th Annual Meeting, Shreveport, Louisiana